In dynamic semiconductor memory storage devices it is essential that storage node capacitor cell plates be large enough to retain an adequate voltage level in spite of parasitic capacitances and noise that may be present during circuit operation. As is the case for most semiconductor integrated circuitry, circuit density is continuing to increase at a fairly constant rate. The issue of maintaining storage node capacitance is particularly important as the density of DRAM arrays continue to increase for future generations of memory devices.
The ability to densely pack storage cells while maintaining required storage capabilities is a crucial requirement of semiconductor manufacturing technologies if future generations of denser memory array devices are to be successfully manufactured.
One important and very effective approach has been by increasing a storage-node cell plate surface area by depositing a rugged surface polysilicon (rugged poly) to serve as the storage-node cell plate. Although rugged poly can effectively double the storage-node cell plate, its deposition and conductive doping presents unique problems that require special considerations.
The unique problems that arise when processing rugged poly stems from the low temperature (approximately 570.degree. C.) required to create the rugged surface area as the poly is being deposited and the nature of the rugged topology itself.
An approximate temperature of 570.degree. C. is required to maintain the optimal rugged surface of the poly. Despite this, a conventional subsequent step of conductively doping the poly plate requires using a relatively high temperature. This temperature is in the neighborhood of 800.degree. C. to obtain a fairly uniform penetration of dopants into even a smooth surfaced poly.
The rugged surface makes it even more difficult to obtain uniform doping and thus requires even a higher temperature then normal. A problem with this is the doping at such a high temperature causes the rugged poly surface to become virtually smooth as the temperature approaches 600.degree. C., thus losing the advantage created by the rugged poly in the first place.
It is these problems of maintaining a rugged poly capacitor plate surface while achieving successful uniform conductive doping of the rugged poly that the present invention addresses.